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Reflections of the pulse wave

Reflections of the pulse wave. Occur whenever there is a change in vessel cross section or stiffness. Local hydraulic impedance. Small. Big. Big. Small. Stiff. Less stiff. Pressure increases Flow decreases. Pressure decreases Flow increases. Stiff. Less stiff.

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Reflections of the pulse wave

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  1. Reflections of the pulse wave Occur whenever there is a change in vessel cross section or stiffness. Local hydraulic impedance

  2. Small Big Big Small Stiff Less stiff Pressure increases Flowdecreases Pressure decreases Flowincreases Stiff Less stiff Positive and negative wave reflections Pressure increases Flowdecreases + - Pressure decreases Flowincreases Less stiff + Stiff Stiff Less stiff -

  3. Reflection coefficient Zc = c/a

  4. How to separate forward and backward traveling waves • Multiple measurements of pressure/flow diameter and numerical processing of data • Total occlusion methods • Impulse methods

  5. Total occlusion method • Measure pressure in region of interest • Apply a total occlusion distal to the region and re-measure pressure • Substitute for P

  6. How to separate forward and backward traveling waves • Multiple measurements of pressure/flow diameter and numerical processing of data • Total occlusion methods • Impulse methods

  7. Impulse method • Generate a sharp spike of pressure/flow and track its movement at different points. • If sharp enough its reflection can be observed in isolation from the incident wave

  8. Measurement of pulse transmission in vivo

  9. Measurement of pulse transmission in vitro

  10. In-vivo or in-vitro

  11. 20 kPa 50 ms Propagation and reflection in a uniform tube Distance 0 Distance 0 100 150 300 200

  12. Wave propagation in arterial models Stenosed artery Normal artery

  13. Reflections at the aorto iliac trifurcation

  14. Pb Pf Pm Pf Pb Vasodilation Reflections in vivo Pm Vasoconstriction Newman DL & Greenwald SE Cardiovascular Research 113: 595-600. (1979) Bertram, CD et al. (1997). Medical Engineering and Physics 19: 212-222.

  15. Do negative reflections occur in the “healthy” vascular system?

  16. Catheter tip manometer Abdominal aorta Effect of age on aorto-iliac reflection coefficient • Post mortem measurements of velocity and area ratios • 46 subjects aged between 3 months and 88 years • Velocity of pressure wave from catheter • Dimensions of junction from radiography Greenwald, S.E. et al. (1990) Circulation82, 114-23.

  17. Effect of age on area & velocity ratio or VR y = -0.0023x + 0.95 R = 0.92

  18. Effect of age on aorto-iliac reflection coefficient

  19. Early reflection augments systolic pressure Pm Late reflection augments diastolic pressure Pm Pb Pb Pf Aortic pressure wave Pf Young Old/Hypertensive Time scale

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